The present invention relates to a light beam scanning apparatus for scanning a plurality of laser beams in an image formation apparatus such as a digital copier or a laser printer which forms a single electrostatic latent image on a single photoconductor drum by simultaneously performing scanning and exposure on the photoconductor drum by using the plurality of laser beams.
In recent years, there have been developed various digital copiers according to scanning and exposure using a laser light beam (hereafter referred to as the light beam) and an electrophotographic process.
Recently, a multi-beam digital copier is developed for increasing an image formation speed. The multi-beam system generates a plurality of light beams and simultaneously scans a plurality of lines using these light beams.
Such a multi-beam digital copier is equipped with a semiconductor laser oscillator for generating a plurality of light beams and an optical unit as a light beam scanning apparatus. The optical unit chiefly comprises a rotating polygon such as a polygon mirror, a collimator lens and an f-xcex8 lens for reflecting each light beam from the plurality of laser oscillators toward a photoconductor drum and scanning on a photoconductor drum using each light beam.
Conventionally, the optical unit of the multi-beam digital copier controls scanning direction exposure positions and passage positions of light beams. The scanning direction exposure position control relates to controlling light beam positions in a main scanning direction. The passage position control relates to controlling light beam positions in a sub-scanning direction.
An exemplification of this technology is proposed in U.S. patent application Ser. No. 9/667,317. According to the exemplification, a pair of sensors detect passage points of light beams scanning a photoconductor drum surface in the sub-scanning direction in order to control light beam positions by detecting light beams with high precision in a wide range. The pair of sensors are arranged at a position equivalent to the surface to be scanned. Each of the pair of sensors is formed of a trapezoid pattern, for example. The pair of sensors are arranged symmetrically to each other with a specified interval.
A light beam scanning position is determined by a value obtained by integrating output differences from the pair of sensors. A processing circuit connected to the pair of sensors computes an integration value indicative of the light beam scanning position. The processing circuit comprises a plurality of operational amplifiers and uses an integrator to integrate an electric signal difference detected by each sensor.
U.S. patent application Ser. No. 9/816,773 proposes a pair of sensors comprising two sawtooth patterns for detecting a light beam. Like U.S. patent application Ser. No. 9/667,317, the proposal in Ser. No. 9/816,773 determines a light beam scanning position by using the processing circuit for integrating output differences from the pair of sensors.
In the case of a saturated output from the processing circuit for processing an output signal from the pair of sensors, U.S. patent application Ser. Nos. 9/667,317 or 9/816,773 proposes detection of a light beam scanning position by correcting an output signal from the pair of sensors.
However, there is not provided control to effectively determine a correction amount for correcting an output signal from the pair of sensors. If the light beam excessively deviates from the center position, for example, repeating the correction using a minimum correction amount makes the correction process time-consuming.
Further, an offset voltage exists in the processing circuit for processing an output signal from the pair of sensors. There is the problem that such an offset voltage in the processing circuit affects determination of a light beam passing position.
It is therefore an object of the present invention to provide a light beam scanning apparatus which can effectively determine a light beam scanning position.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; a processing circuit which has a plurality of operational amplifiers, corrects an output from each of the pair of sensors, and integrates a difference between these corrected electric signals; a control section which determines the necessity of correction based on a value integrated by this processing circuit, determines a scanning position of the light beam according to a value integrated by the processing circuit when the necessity of correction is not determined, and sets a correction amount based on a value integrated by the processing circuit and an offset amount present in the processing circuit when the necessity of correction is determined; and a correction signal generation circuit which outputs a correction signal to the processing circuit so as to correct an electric signal output from each of the pair of sensors based on a correction amount set in this control section.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; an integrator circuit which integrates a difference between electric signals output from each of the pair of sensors; a first comparator circuit which compares a value integrated in this integrator circuit with a first threshold; a second comparator circuit which compares a value integrated in the integrator circuit with a second threshold smaller than the first threshold; and a control section which specifies first and second thresholds to the first and second comparator circuits, when the comparator circuits yield a normal comparison result, determines an output value of the integrator circuit according to magnitude relation between the first and second thresholds, and, when the comparator circuits yield an abnormal comparison result, determines whether the offset has an effect on the abnormal comparison result based on the predetermined maximum offset amount.
A light beam scanning apparatus according to the present invention comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; an integrator circuit which integrates a difference between electric signals output from each of the pair of sensors; a first comparator circuit which compares a value integrated in this integrator circuit with a first threshold; a second comparator circuit which compares a value integrated in the integrator circuit with a second threshold smaller than the first threshold; and a decision section which specifies first and second thresholds to the first and second comparator circuits, uses the first and second comparator circuits to repeat comparison among the integrator circuit""s output value and the first and second thresholds for a plurality of times, and determines magnitude relation among the integrator circuit""s average output value and the first and second thresholds based on the number of times for determining the integrator circuit""s output value to be greater than the first threshold, the number of times for determining the integrator circuit""s output value to be between the first and second thresholds, and the number of times for determining the integrator circuit""s output value to be smaller than the second threshold.
An image formation apparatus according to the present invention has an image support to form a latent image on a scanned face where a light beam is scanned based on image information and image formation means for forming an image formed on this image support onto an image formation medium. The image formation apparatus comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan the light beam toward a scanned face so that the light beam scans the scanned face on the image support in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; a processing circuit which has a plurality of operational amplifiers, corrects an output from each of the pair of sensors, and integrates a difference between these corrected electric signals; a control section which determines the necessity of correction based on a value integrated by this processing circuit, determines a scanning position of the light beam according to a value integrated by the processing circuit when the necessity of correction is not determined, and sets a correction amount based on a value integrated by the processing circuit and an offset amount present in the processing circuit when the necessity of correction is determined; and a correction signal generation circuit which outputs a correction signal to the processing circuit so as to correct an electric signal output from each of the pair of sensors based on a correction amount set in this control section.
An image formation apparatus according to the present invention has an image support to form a latent image on a scanned face where a light beam is scanned based on image information and image formation means for forming an image formed on this image support onto an image formation medium.
The image formation apparatus comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; an integrator circuit which integrates a difference between electric signals output from each of the pair of sensors; a first comparator circuit which compares a value integrated in this integrator circuit with a first threshold; a second comparator circuit which compares a value integrated in the integrator circuit with a second threshold smaller than the first threshold; and a control section which specifies first and second thresholds to the first and second comparator circuits, when the comparator circuits yield a normal comparison result, determines an output value of the integrator circuit according to magnitude relation between the first and second thresholds, and, when the comparator circuits yield an abnormal comparison result, determines whether the offset has an effect on the abnormal comparison result based on the predetermined maximum offset amount.
An image formation apparatus according to the present invention has an image support to form a latent image on a scanned face where a light beam is scanned based on image information and image formation means for forming an image formed on this image support onto an image formation medium. The image formation apparatus comprises: a light emitting device which outputs a light beam; a light beam scanning member which allows a light beam output from this light emitting device to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of sensors which are arranged on the scanned face or a position equivalent thereto, detect a light beam scanned by the light beam scanning member, and output an electric signal; an integrator circuit which integrates a difference between electric signals output from each of the pair of sensors; a first comparator circuit which compares a value integrated in this integrator circuit with a first threshold; a second comparator circuit which compares a value integrated in the integrator circuit with a second threshold smaller than the first threshold; and a decision section which specifies first and second thresholds to the first and second comparator circuits, uses the first and second comparator circuits to repeat comparison among the integrator circuit""s output value and the first and second thresholds for a plurality of times, and determines magnitude relation among the integrator circuit""s average output value and the first and second thresholds based on the number of times for determining the integrator circuit""s output value to be greater than the first threshold, the number of times for determining the integrator circuit""s output value to be between the first and second thresholds, and the number of times for determining the integrator circuit""s output value to be smaller than the second threshold.
A light beam scanning apparatus according to the present invention comprises: light emitting means for outputting a light beam; light beam scanning means for allowing a light beam output from this light emitting means to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of detection means, arranged on the scanned face or a position equivalent thereto, for detecting a light beam scanned by the light beam scanning member and outputting an electric signal; processing means having a plurality of operational amplifiers for correcting an output from each of the pair of detection means and integrating a difference between these corrected electric signals; control means for determining the necessity of correction based on a value integrated by this processing means, determining a scanning position of the light beam according to a value integrated by the processing means when the necessity of correction is not determined, and setting a correction amount based on a value integrated by the processing means and an offset amount present in each operational amplifier in the processing means when the necessity of correction is determined; and correction signal generation means for outputting a correction signal to the processing means so as to correct an electric signal output from each of the pair of detection means based on a correction amount set in this control means.
A light beam scanning apparatus according to the present invention comprises: light emitting means for outputting a light beam; light beam scanning means for allowing a light beam output from this light emitting means to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of detection means, arranged on the scanned face or a position equivalent thereto, for detecting a light beam scanned by the light beam scanning means and outputting an electric signal; integration means for integrating a difference between electric signals output from each of the pair of detection means; first comparison means for comparing a value integrated in this integration means with a first threshold; second comparison means for comparing a value integrated in the integration means with a second threshold smaller than the first threshold; and control means for specifying first and second thresholds to the first and second comparison means, when the comparison means yield a normal comparison result, determining an output value of the integration means according to magnitude relation between the first and second thresholds, and, when the comparison means yield an abnormal comparison result, determining whether the offset has an effect on the abnormal comparison result based on the predetermined maximum offset amount.
A light beam scanning apparatus according to the present invention comprises: light emitting means for outputting a light beam; light beam scanning means for allowing a light beam output from this light emitting means to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; a pair of detection means, arranged on the scanned face or a position equivalent thereto, for detecting a light beam scanned by the light beam scanning means and outputting an electric signal; integration means for integrating a difference between electric signals output from each of the pair of detection means; first comparison means for comparing a value integrated in this integration means with a first threshold; second comparison means for comparing a value integrated in the integration means with a second threshold smaller than the first threshold; and decision means for specifying first and second thresholds to the first and second comparator means, using the first and second comparison means to repeat comparison among the integration means"" output value and the first and second thresholds for a plurality of times, and determining magnitude relation among the integration means"" average output value and the first and second thresholds based on the number of times for determining the integration means"" output value to be greater than the first threshold, the number of times for determining the integration means"" output value to be between the first and second thresholds, and the number of times for determining the integration means"" output value to be smaller than the second threshold.
A method of detecting a light beam passage position according to the present invention comprises: generating a light beam; allowing a generated light beam to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; converting a light beam scanning the scanned face to an electric signal by using a pair of sensors arranged on the scanned face or a position equivalent thereto; correcting an electric signal converted from each of the plurality of sensors based on a correction signal and integrating a difference between these corrected electric signals by using a processing circuit having a plurality of operational amplifiers; determining the necessity of correction based on the integrated value, determining a scanning position of the light beam according to a value integrated by the processing circuit when the necessity of correction is not determined, and setting a correction amount based on a value integrated by the processing circuit and an offset amount present in the processing circuit when the necessity of correction is determined; and outputting a correction signal to the processing circuit so as to correct an electric signal output from each of the pair of sensors based on the set correction amount.
A method of detecting a light beam passage position according to the present invention comprises: generating a light beam; allowing a generated light beam to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; converting a light beam scanning the scanned face to an electric signal by using a pair of sensors arranged on the scanned face or a position equivalent thereto; integrating a difference between electric signals converted by each of the pair of sensors; comparing the integrated value with a first threshold by using a first comparator circuit; comparing the integrated value with a second threshold smaller than the first threshold by using a second comparator circuit; and specifying first and second thresholds, when the comparator circuits yield a normal comparison result, determining magnitude relation between the first and second thresholds, and, when the comparator circuits yield an abnormal comparison result, determining whether the offset has an effect on the abnormal comparison result based on the predetermined maximum offset amount.
A method of detecting a light beam passage position according to the present invention comprises: generating a light beam; allowing a generated light beam to scan toward a scanned face so that the light beam scans the scanned face in a main scanning direction; converting a light beam scanning the scanned face to an electric signal by using a pair of sensors arranged on the scanned face or a position equivalent thereto; integrating a difference between electric signals converted by each of the pair of sensors by using an integrator circuit; comparing the integrated value with a first threshold by using a first comparator circuit; comparing the integrated value with a second threshold smaller than the first threshold by using a second comparator circuit; and specifying first and second thresholds, repeating comparison among the values integrated by the first and second comparator circuits and the first and second thresholds for a plurality of times, and determining magnitude relation among an average value of the integrated values and the first and second thresholds based on the number of times for determining the integrated value to be greater than the first threshold, the number of times for determining the integrated value to be between the first and second thresholds, and the number of times for determining the integrated value to be smaller than the second threshold.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.